Method for the pyrolysis of diacyl cyanides



Dec. 22, 1953 L. F. REUTER ETAL METHOD FOR THE PYRoLYsIs 0F DIACYL CYANIDEs Filed May '7, 1952 aina .62u30 www1. A

Patented Dec. 22., 1953 UNITED stares sr cerise( a .corporation .ifNew York 'diacyl ecyanides to ygivre monomeric :Vinylene ser .methylene imalononitrile) v4or f'on'e -of its homologs is A'obtained and rpertains .more partic- .-.u1'ar.ly `:tjo a jprocess whereby :diacul cyanides fare `pyrolytically sdecarhoxylated in an '.eiiicient mam .ner in high fyield at .atmospheric pressure @Withiout attendant .'losses fof the Ydesired .monomeric product.

.it is .-.disclosed :in "El, 1S. .Patent 234176,27() .that .thediacylf cyanide, .l-.acetoXy-.l,ledicyano fethane, can he pyrolgyzed .-at temperatures `of 400 C. Vto .'ZObiC. to :give :monomeric vinyl-idene scyanide, an extremely valuable polymerizable material which =is especially useful fin :the preparation oi ,polio-ners and linterpolyrners suitable --as syn- -thetic fbers, synthetic -resins and AplasticsVV However, unless .the process as described iin the patent is fcarried .out at reduced pressures, gpreferably 2 to :510 .-mrn. of mercury, the bylield 1oi' the desired monomeric vinylidene :cyanide is not :as .high as is :desirable and -carbon-ization :of .the pyrolysis tube occurs to a .con-- siderable .extent. This dependency onreduced .pressure for optimum .results .is .quite undesir- .ableior a numbenof .-reasons. Forexample, the production and vmaintenance .of such ia vacuum .involves .the installation .of expensive equipment .and .the .necessity .-for close operational control both vof which add .materially to the initial cost and .up-keep of .the pyrolysis plant. Also, .re- -.duced pressure makes necessary :on a ,.-large scale the use of a large .pyrolysis .tube fand-or .a .high .temperature `and limits .severely the amount of pressuredrop through the -pyrolysis tube. 'Ilhese conditions .in turn .lead to -a pronounced temperiature drop across .the tgas .film .at the `pyrolysis .tube interface withattendant lo-vercraclring along the vtube IWalls and reduced stabiliti7 Aof the ,Dy- `rolysis viproduct. Additionally, .reduced .pressure ,pyrolysis requires the use 4of very .low .temperatures for ,pyrolysis ,product condensation, this factor .again .adding to the .cost .of Aa .pyrolysis plant. Also, the reduced kpressure process vis .not Well suited for .use 'on .a vcontinuous scale. As a .result .of these disadvantages, ther .process .specifi- -cally described in Il. S..Patent .2,476,270 iis .not Yas well suited for .practical commercial usage .as .is desired.

Accordingly, it .lis .1an object of the `.present invention to ,provide a process whereby V1aeetoxy 1,1-.dicyano l.etnane .(Idiacetyl .cyaniiieI .as well 6 Claims. (Cl. 2260-4653) .52 as .other .di-acyl eyanides, .may be .readily .and aconomically .pyrlyzed .at atmospheric Apressure 'to ,.giue lhigli Lyields 0L-monomeric ivinylidene `civanide or -alhomolog thereof. y n

llt -is .another iob'ject of the invention i.togproiv'ide a continuous .process whereby idiaoylrcyaini'des .can The .pyrolyzed .at y` substa,ntially :atmospheric pressure -and* .in `such La manner vthat e stable .ptyrolysis 7product `comprising `the desired .-monomer `can `be continuously .recovered 'trom the.processin'highyields- 3ft lis .still another object .of the-.invention to provide a oon'tnuous ,process whereby `.diatn'l -`cyarides :can be A`pyrolyt'ically deacyloxyated, and .the .resulting ip yrolys'is Vvapors -condensed 'Without the .occurrencezof substantial polymerization of lthermenomers .presen'tn the pyrolys'lis product. .Dther objects -o'f Ltheinyention will be .apparent from the .description :which .follows It 'has now been .discovered .that the .above and .other biedts may 'b'e readily attained `bya proc- .ess Ainvol-virng: 'the stepsV of iirst :vaporiz'ing Ithe diacyl cyanide, .pyrlyz'ing. .the vapors, linstantane'ously quenching the hot ,pyrlyysis product vapors with 'large volume, .as compared .to lthe volume of the vaporso'f a .liquidstream .of cold pyrolys'ls .product .or a diluent liquid .or a mix- 'fture .off both, 'thereby .simultaneously yremoving the .condensed pyrlysis ,product from the=qunh zione. By .carrying out .theipyrolysis ,process in this manner 'it 'is possible to 'operate at .atmospheric pressure or .at pressures .slightly .above Latmospheric and yet obtain very 'High convers'lo'ns .o di'acsl cyanide to monomeric ii'iilfidene *cyanide 'or homolog, with 'only negligible polymerization of the desired monomer, 'or car'- lprocess' can 'be operated' continuously and economica-Hy itc give consistently nigh yields 'of the les'ireii 'monomeric 4rvir'iylii'ene cyanide or homol 'The pyrolysi's o'f d'iacyl 'cy'ariides raccordiii' to nthe process :of 'the present 'invention `fprciceelsi'' substantially asfilows:

'nhere'inn is .an acvloxy radical, uoreferati-y 'confrom 2 to A6 carbon atoms, 2vand li/isfh'y-y 3 and carboxylic acid whereas when R is lower alkyl there is obtained, in pla-ce of vinylidene cyanide, a homolog thereof of the formula E CN C/ i' NJN 'Ihe temperature at which the pyrolysis process is carried out may be varied widely. For example, temperatures as low as 300 C. or lower to 800 C. or even higher are operative. However, temperatures in the range of 500 C. to 600 C. are especially preferred since temperatures above about 600 C. sometimes lead to "overcracking of the diacyl cyanide accompanicd by substantial polymerization of the monomer. At temperatures below about 500 C. the pyrolysis proceeds quite slowly and requires a large pyrolysis tube in order that the process -be operated efficiently.

It is desirable but not absolutely essential to carry out the pyrolysis in the presence of an inert diluent material which may be either a gas or a liquid at room temperature. The use of such a diluent, especially one which is a liquid at room temperature, is advantageous in that it eliminates the need for installation of a diacyl cyanide drier and lowers the melting point of the feed, so that less heat treatment for the molten diacyl cyanide'in the feed system is required, and the dew point of the pyrolysis product vapors is lowered. Also, the use of a diluent lowers the partial pressure of vinylidene cyanide in the condensed pyrolysis product vapors. The diluent material which is utilized may be any material which is inert toward both the diacyl cyanide and the monomeric vinylidene cyanide or homolog, i. e., it must neither react with nor affect in any substantial manner said compounds at any stage of the pyrolysis process. Included among the substances which are inert toward diacyl cyanides and monomeric vinylidene cyanide and its homologs are the liquid aromatic hydrocarbons or halogen substituted aromatic hydrocarbons such as'benzene, o, m, or p-toluene, o, m, or p-xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene and the like. Inert diluent gases which may be utilized include methane, ethane, propane, nitrogen, hydrogen and` helium as well as mixtures of such gases and the like. It is to be understood, of course, that the inert dluents disclosed above do not represent all of the inert substances which can be utilized. It is also to be understood that the use of an inert diluent, while desirable for the reasons set forth hereinabove, is not a critical expedient in the present process.

Proper and rapid condensation of the pyrolysis product vapors is highly important to the successful operation of the atmospheric pressure pyrolysis process. The condensation is best carried outby directing the pyrolysis product vapors from the pyrolyzer into a quench zone which desirably is a quench nozzle of restricted volume where the hot vapors are met with va relatively large liquid flow of preformed pyrolysis product or an inert liquid diluent, or a mixture of both, maintainedA at a temperature no higher than room temperature hereinafter referred to as being cold because of its low temperature in relation to that of the hot pyrolysis vapors. The vcold flow of liquid instantaneously condenses the pyrolysis product vapors and removes the condensate from the quench zone immediately, so that the condensate is not in contact with hot vapors for more than an instant. Prolonged contact with hot vapors which causes polymerization of the monomer, reduction in yield of the desired product, as well as plugging of the pyrolysis system, is thus eliminated. In order that polymerization will be held at a minimum, it is important that the pyrolysis vapors be maintained above the dew point until the exact moment at which they are contacted by the cold flow of quench liquid. This is readily accomplished by heating the line through which the vapors pass from the pyrolyzer to the quench nozzle.

As disclosed hereinabove, the use of large quantities of quench liquid is important in the present process. Accordingly, it is desirable that the ratio of quench liquid to pyrolysis product vapors be at least 50 to l on a weight basis, and preferably nearer 200 to 1, although higher or lower ratios mayalso be utilized. This ratio may be controlled accurately either by adding liquid diluent to the diacyl cyanide fed into the pyrolyzer or by adding the diluent to the quench liquid continuously.

It is also desirable that an inhibitor of polymerization be incorporated in the liquid pyrolysis product either simultaneously with the condensation process or as soon as possible after condensation of the pyrolysis vapors in order that the polymerization of the monomeric vinyllidene cyanide will not be initiated by other of the materials present in the pyrolysis product mixture. Many of the commonly used polymerization inhibitors such as hydroquinone, phenyl betanaphthylamine and the copper salts are not useful for this purpose since they actually catalyze the polymerization of monomeric vinylidene cyanide. However, certain other'materials are useful for inhibiting the polymerization of monomeric vinylidene cyanide. Such materials include sulfuric acid, preferably of a concentration of or higher, the halosulfonic acids such as chlorosulfonic acid, the sulfonyl chlorides Such as toluene sulfonyl chloride or benzene sulfonyl chloride, sulfur dioxide and the like. Only catalytic quantities of inihibitor are utilized; for example, amounts of from 0.01% to 2% of stabilizer, based on the weight of the crude pyrolysis product, give excellent results. Larger amounts are not desirably utilized since reduced pyrolysis product stability is likely to result.

The pyrolysis of diacyl cyanides in accordance with the present invention will be described in greater detail below. Reference is also made to the accompanying drawing which is a diagrammatic illustration of a preferred method for carrying out the pyrolysis process.

, Referring to the drawing, there is shown a` melt tank I into which diacyl cyanide and diluent, if one is utilized in the diacyl cyanide feed, are supplied through feed inlet 2. The diacyl` cyanide and diluent, if any, are heated to about. 100 C. by steam in jacket 3 and the resulting;

hot solution is blown by pressure at feed inlet 2. through line l into feed tank 5, which is heated by hot water in jacket 6. The hot diacyl cyanide (or diacyl cyanide solution if a solvent is utilized) then discharges through basket strainer ,'i where any tarry residue is removed and is then fed by metering pump S through rotameter 9 and into vaporizer l0. In the Vaporizer I0, the diacyl cyanide feed is vaporized and maintained at a temperature of about 260 C. by heat supplied by electrical heating coil Il which is supplied with electrical energy at source I2. The heated vapors then pass through tar trap I3 where any tarry materials are removed so as to prevent plugging of line N through which the vapo-rs enter' the pyrolyzer I5'. Line' |`4- is preferably heated to prevent condensation of the vapors and tomaintain the temperature of the vapors at about 250.6' as' they enter the pyrolyze'r. In pyroly'zer t5 helical coiled tubing IG, preferably constructed of stainless steel o'r other corrosion resista-nt materiali is surrounded by a lead bathA heated to the pyrolysis temperature by electrical heater ffl, supplied withv electrical'ehergy source` |18. the' vapors from vaporizer lo pass: through the heated helical coiled tube itl theya're thermally decomposed intov monomeric vinylidene cyanide or homolog, a' carboxylic acid and icy-products. These pyrolysis product vapors, which also con-- tain some unreacted diacyl cyanide and diluent, ifi one is utilized, pass through line la' which is desirably heated to'- prevent condensation of the pyrolysis product vapor,- into quench nozzl'el2ll. the quench nozzie 2i?, the pyrolysis product vapors are condensed instantaneously by a large ow of crude p'yrolysis' prc'iduct pumped' from t'anliv 2| by pump 22 through basket strainer 23 (to remove tarry residue), quench cooler' 24v where heat taken up in the quenching' operation is removed, line and vent gas scrubber 2t. The quench nozzle 20 is so designed that the vapors are kept at antemperatur'e above their dew' point until they enter the' quenching zone. Non-coni dens'able gases (nitrogen, carbon dioxide and the ilgze)v pass upward through the vent gas scrubber 26 where the downward flow of cold quench liquid removes substantially all of the monomeric vinylidene cyanide or homolog from the gases before A they are vented to the atmosphere. The downward now of large quantities offquench liquid through vent gas scrubber 2'3 and through quench nozzle 2S removes the condensed pyrolysis product from the quenching zone immediately after Y As disclosed hereinabove, it is desirable that an inhibitor be added to the crude liquid pyrolysis product in order to prevent polymerization of the monomeric vinylidene cyanide after it is removed from the quench zone. The inhibitor is added to the crude pyrolysis product either in quench nozzle 2U or tank 2 l, or both, being drawn from storage tank 21 and fed by metering pump 28 through lines 29 and/or y3l) into the crude liquid pyrolysis product. The crude Apyrolysis product is removed from the quench system continuously and fed through lines 3l into the crude pyrolysis product storage tank 32 which is cooled by a refrigerant which is continuously passed through coil 33.

The'crude liquid pyrolysis product in tank 32 may be used as such or may be drawn ofi through purication line 34 and purified by distillation or by one of several other methods. For example, monomeric vinylidene cyanide can be recovered from the crude pyrolysis product in substantially pure form by treating the pyrolysis product with Conversion-:

a conjugated diolenh' such: as butadiene eyeing pentadiene which reacts with the monomeric vinylidene cyanide to form a solid:` substituted' cyclohexene whichvcan be separated from the carboxylic acid and other impurities and pyrolyz'ed' at temperatures in" excess`l of. about 460y C. toV give monomeric vinylidene cyanide the conjugated' diolenn.

Alternatively, the vinylidene cyanide can be recovered by pouring the liquid product into Vvvatert'o bringabout'its polymerization, after which the solid polymer can be easily separated from the' liquid materials by filtration or decarrtae tion. The polymerized vinylidene cyanide can vbe depol-ymerized by pyrolysi's, preferably at temperatures of C. to 2509 C., to give monomeric vinylidene cyanide, a process described'more fully in U. S. Patent 2,535,827.

The following examples illustrate in detail the preparation of pyrolysis product comprising `monomeric vinylidene cyanide according tothe process of the present invention. The examples are not intended to limit the invention, how.n ever, for there are, of course, numerous possible Variations: and modications in the procedures described. In the examples all parts are by weight.

Example Referring again to the accompanying drawing; l-acetoxy-Ll-dicyano ethane is melted in tank- I' and passed, together with monochlorobenzene into feed tank 5. From the feed tank thev solution is pumped into vaporizer i0 at such a rate that 3.33 parts of l-acetoxy1,1-d-icyano ethane are fed into the vaporizer each hour, together with about 0.5 part of monochlorobenzene per part of the diacyl cyanide. Vapors from I' pass into pyrolyzer I5 which contains a stainless steel helical coil, 40 feet in length, with a 1%; inch outside diameter and a wall thickness of 0.049 inch. In the pyrolyzer the leacetoxy-Ll-dicyano etha'ne vapors are pyrolytically deacetoxylated at a temperature of 530 C. The crude pyrolysis product vapors then pass through line i9 into quench `nozzle 2c Where the vapors are met with a large downward ilow of a mixture of monochlorobenzene and condensed crude pyrolysis product which is cooled by service water" in quench liquid cooler 24 and pumped through line 25 and vent gas scrubber 26. The downward now of quench liquid quickly flushes the conh densed vapors from the condensing zone and thus prevents prolonged contact of condensed pyrolysisA product with heated vapors from the pyrolyzer and consequently polymerization of the monomeric vinylidene cyanide in the condensate is substantially eliminated.

Sulfuric acid, to further aid in inhibiting the polymerization of monomeric vinylidene cyanide, is continuously metered from acid storage 21 into the quench nozzle and/or the quench'liquid Stor age tank. The ilow of acid is adjusted so that the crude pyrolysis product in storage tank 2| contains about 0.61% by Weight ofthe acid.

The liquid pyrolysis product, which contains 28.4% of monomeric vinylidene cyanide, is con* tinuously withdrawn through line 3| into refrigerated tank 32, from which the product canV be purified or utilized in the crude form in polyerneriz'ations. A conversion of 97.1% is obtained, the' conversion being calculated according to the following formula:

. lQiacyl cyanidefed to pyrolyzer The yield of monomeric vinylidene cyanide,'based on the quantity of diacyl cyanide fed to the pyrolyzer, is 80.7%.

Examples II `to IV 1-acetoxy-1,1dicyano ethane is pyrolyzed according to the general method of Example I except that the pyrolysis conditions are varied in order to demonstrate the effect of varying temperatures, feed rates and quantity of diluent. The operational data are recorded in the table below.

Example II III IV Weight percent l- 66.7....L 100 (no dilu- 66.7. acetoxy-l,l ent).

dicyano ethane infeed. l Parts 1-acetcxy- 6.67 l0.0 6.67.

-1,1dicyano ethane fed per rirysis tube in' it" o 27' if," o so' x 84,-" o

size. D., 0.049 D., 0.040 D., 0.049"

Wall th. wall th. wall th. Weight ratio of 100 50 0.

quench medi- Yum to vapors. Tnciperature, 560 520 535. Inhibitor 0.01% sulfuric 0.01% chloro- 0.01% sulfuric acid. sullonic acid. scid. Percent conver- 99.1 95.8.

sion. Percent yield 79.9 84.0 00.3.

Monomeric vinyudene cyanide or a homolog thereof is also obtained in very goed yields when other diacyl cyanides of the structure set forth hereinabove, for example, 1-propionoxy1,1di

cyano propane, l-propicnoxy-1,1-dicyano ethane,

or,1acetoxy-1,1dicyano butane, are substituted for l-acetoXy-1,1-dicyano ethane in the examples. Also, when other temperatures in the range of l300" C. to 800 C. are utilized or when the process is carried out utilizing other of the diluents disclosed hereinabove, the process operates emciently to give high yield or the desired products.

y Although specic examples of the invention have been herein described, it is not intended to limit the invention solely thereto, but to inciudc all of the variations and modications falling Awithin the spirit and scope of the appended vclaims.

` We claim:

1. In the method for the preparation of monomeric 1,1-dicyano ethylene and its lower alkyl 2- substituted homologs by the vapor phase pyrolytic deacyloxyation of a diacyl cyanide at a temperature of 300 to 800 C., lthe step of rapidly condensing the hot pyrolysis vapors by bringing a stream oi hot pyrolysis vapors into concurrent flow with a moving stream of a cold inert quench liquid, the weight ratio of quench liquid to pyrolysis product being at least 50 to 1 and the said quench liquid containing an inert liquid aromatic compound and being at a temperature not higher than room temperature.

` 2. In the method oi preparing monomeric 1,1- dicyano ethylene by the vapor phase pyrclytic Ideacetylation of 1acetoxy-i,1dicyano ethane at atmospheric pressure and at a temperature of `500 to 600 C., the improvement which comprises :rapidly condensing the pyrolysis product vapors by bringing a stream thereof at a temperature above the dew point of said vapors into concurrent flow with a moving stream of a cold inert quench liquid selected from the class consisting of liquid aromatic hydrocarbons and liquid halogenated aromatic hydrocarbons, the Weight ratio of said quench liquid to pyrolysis nroduct be- 8 ing at least 50 to 1 and the said quench liquid being at a temperature not higher than room temperature, and rapidly removing the condensed pyrolysis product and quench liquid from contact with hot incoming pyrolysis vapors.

3. The method of claim 2 in which the quench liquid comprises a mixture of the cooled condensate resulting from the pyrolysis at 500 to 600 C. of 1-acetoxy1,ldicyano ethane and condensing the eiiiuent vapors, and at least one other liquid selected from the class consisting of liquid aromatic hydrocarbons and liquid halogenated aromatic hydrocarbons.

4. In the method of preparing 1,1-dicyano ethylene by the vapor phase pyrolytic deacetylation of 1acetoxy1,1dicyano ethane at a temperature of 300 to 800 C., the improvement which comprises vaporizing a solution of said l-acetoxy- 1,1-dicyano ethane in an inert solvent selected from the class consisting of liquid aromatic hydrocarbons and liquid halogenated aromatic hydrocarbons, pyrolyzing the resultant vapors at atmospheric pressure and at a temperature of 300 to 800 C. whereby said 1,1-dicyano ethylene is formed, rapidly condensing the pyrolysis product vapors by bringing a stream thereof, at a temperature above the dew point of said vapors, in concurrent flow with a moving stream of a cold inert quench liquid containing an inert aromatic liquid, the Weight ratio of quench liquid to pyrolysis product being at least 50 to 1 and the temperature of said quench liquid being not in excess of room temperature, and rapidly flowing the combined stream of pyrolysis condensate and quench liquid away from contact with hot incoming pyrolysis vapors.

5. In the method of preparing 1,1-dicyano ethylene by the vapor phase pyrolytic deacyloxyation of 1acetoxy-l,1dyciano ethane at atmospheric pressure and at a temperature of S00 to 800 C., the improvement which comprises rapidly condensing the pyrolysis product vapors by bringing a stream thereof into concurrent flow with a moving stream of a cold inert quench liquid containing an inert aromatic compound, the Weight ratio of quench liquid to pyrolysis product being at least 50 to 1 and the said quench liquid being at a temperature not higher than room temperature, adding to the condensate as it forms an inhibitor selected from the class consisting of sulfuric acid, and chlorosulfonic acid, and rapidly flowing the combined stream of pyrolysis condensate, quench liquid and inhibitor from further contact with hot incoming pyrolysis vapors.

E. The method of claim 5 in which the quench liquid is a mixture of monochlorobenzene and the cooled pyrolysis condensate obtained from the pyrolysis at 500 to 600 C. of l-acetoxy-Ll-'dicyano ethane and condensing the eiluent vapors, and the inhibitor is sulfuric acid.

' LOUIS F. REUTER.

RICHARD D. SMITH.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,444,882 Tawney July 6, 1948 2,467,373 Dutcher et al Apr. 19, 1949 2,467,378 Gilbert Apr. 19, 1949 2,471,927 Bortnick et al May 31, 1949 2,476,270 Ardis July 19, 1949 2,535,827 Ardis et al. Dec. 26, 1950 

1. IN THE METHOD FOR THE PREPARATION OF MONOMERIC 1,1-DICYANO ETHYLENE AND ITS LOWER ALKYL 2SUBSTITUTED HOMOLOGS BY THE VAPOR PHASE PYROLYTIC DEACYLOXYATION OF A DIACYL CYANIDE AT A TEMPERATURE OF 300 TO 800* C., THE STEP OF RAPIDLY CONDENSING THE HOT PYROLYSIS VAPORS BY BRINGING A STREAM OF HOT PYROLYSIS VAPORS INTO CONCURRENT FLOW WITH A MOVING STREAM OF A COLD INERT QUENCH LIQUID, THE WEIGHT RATIO OF QUENCH LIQUID TO PYROLYSIS PRODUCT BEING AT LEAST 50 TO 1 AND THE SAID QUENCH LIQUID CONTAINING AN INERT LIQUID AROMATIC COMPOUND AND BEING AT A TEMPERATURE NOT HIGHER THAN ROOM TEMPERATURE. 